Note 10 - Stockholders' Equity (Details Textual) - USD ($)					3 Months Ended	12 Months Ended
	Oct. 23, 2017	Oct. 11, 2010	Jan. 05, 2009	May 16, 2008	Dec. 31, 2015	Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016		Sep. 21, 2012	Sep. 29, 2009	Sep. 28, 2009	Jan. 08, 2009
Stock Compensation Expense Related to Royalties and Stock Bonuses Accrued But Not Issued						$ 3,000
Stock Issued During Period, Value, Share-based Compensation, Gross						372,000	[1],[2],[3]	$ 19,360,000	[4]	$ 686,000	[5]
Stock Issued During Period, Shares, New Issues	7,392,856
Shares Issued, Price Per Share	$ 2.80
Proceeds from Issuance or Sale of Equity, Total	$ 18,900,000							$ 18,905,000
Common Stock, Par or Stated Value Per Share						$ 0.001		$ 0.001
Stock or Unit Option Plan Expense						$ 0		$ 0		$ 200,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross						0		0		0
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant						0
2008 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized				1,500,000									3,000,000	1,500,000
2008 Equity Incentive Plan [Member] | Incentive Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Purchase Price of Common Stock, Percent				110.00%
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period				10 years
2009 Equity Incentive Plan (Executive) [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized		3,060,382
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized												330,000			4,200,000
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period			10 years
Common Stock, Par or Stated Value Per Share															$ 0.001
Over-Allotment Option [Member]
Stock Issued During Period, Shares, New Issues	964,285
Consultant For Strategic Investor Marketing Services [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized						150,000
Director [Member]
Share-based Compensation, Total					$ 38,000
Cash Less Warrant [Member]
Proceeds from Issuance of Common Stock						$ 0
Prepaid Expenses [Member]
Stock Issued During Period, Value, Share-based Compensation, Gross						$ 24,000		$ 24,000
Accounts Payable and Accrued Liabilities [Member]
Share-based Compensation, Total								170,000		$ 176,000
Other Expense [Member]
Bonus and Royalty Accrued and Expensed								$ 170
Share-based Compensation, Total					$ 366,000					$ 176,000

[1] Excludes $24 thousand of stock compensation for stock issued in 2017 that was amortized from prepaid expense in 2018.

[2] The second phase of a 2014 consulting agreement could result in up to an additional 150,000 shares of common stock being granted subject to sales related performance criteria being achieved. At December 31, 2018, those criteria have not been achieved and no shares have been granted for the second phase of the agreement.

[3] Total excludes $3 thousand of stock compensation related to royalties that were recorded as expense but not issued and outstanding as of December 31, 2018.

[4] Does not include stock expense of $170 thousand included in accrued liabilities at December 31, 2017 for unissued stock.

[5] Does not include stock expense of $176 thousand included in accrued liabilities at December 31, 2016.